The smoke stacks at American Electric Power's Mountaineer coal power plant in New Haven, West Virginia.

SAUL LOEB/AFP/Getty Images

Shed a tear for Mr. Coal. This is a historic moment. For most of the past century, coal-fired power plants generated the electricity that lit our cities and powered our factories. And corrupted our politics. But those days are coming to a close. Yesterday, the Environmental Protection Agency issued the first-ever limits on carbon pollution from new power plants, which effectively means that no conventional coal plants will be built in the U.S. again.

The new rules are the culmination of the hotly contested Bush-era Supreme Court ruling that carbon dioxide is indeed a pollutant as defined by the Clean Air Act and that, consequently, the EPA has the authority and duty to regulate it. The rule, now open for public comment for 60 days, will require any new power plant to emit no more than 1,000 pounds of carbon dioxide per megawatt hour of electricity produced – roughly equivalent to the amount of CO2 emitted by a natural gas plant. Coal plants emit about 1,800 pounds of CO2 per megawatt, which means they will be illegal. In theory, new technology called “carbon capture and storage” can be used to reduce carbon pollution from coal plants under the limit, but it’s unproven and expensive. For all intents and purposes, coal is dead as a new power source for 21st-century America.

Politically, the new rule is a big deal, if only because it gives the president a climate-related accomplishment to tout during the campaign, which is especially important after his recent cave-in on the Keystone pipeline. But for Obama it wasn’t a heavy lift. The Supreme Court decision essentially forced the EPA to issue these rules; it was just a question of when. And rising coal prices and the plummeting cost of abundant natural gas prices meant that new coal plants were pretty much dead already. Yesterday’s announcement just puts a stake through their hearts.

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Of course, Republicans will blast Obama anyway, arguing that the rule issued by the “jack-booted Birkenstocks at the EPA” will wreck the American economy and undermine our God-given right to burn fossil fuels. First out of the gate was America’s favorite climate comedian Oklahoma Sen. James Inhofe: “We were successful in stopping their job-killing agenda through legislation when we defeated cap-and-trade,” he said. “Now our fight is to stop them from forcing it on the American people through regulations.”

The real question is this: How much will the new rule actually advance the goal of reducing carbon pollution?

And the answer is, not much – at least not right now. For one thing, the rule applies only to new power plants, not existing plants. So the rule has zero impact on the real problem, which is the 400 or so existing plants in America that dump two billion tons of carbon pollution into the atmosphere every year. EPA is obliged to issue rules for existing plants too, but as David Roberts points out, that is a much tougher call, and one that won’t happen until after the election. (If Mitt Romney wins and/or Republicans take the Senate, a decision will likely be put off for years.)

Secondly, these new rules are a boon for the construction of new natural gas power plants, since these won’t need any controls to meet the standard. (Renewables will benefit too, but to a lesser degree, since they compete less directly with coal, which is used for baseload power; and of course there will be the usual noises about a comeback for nukes). And while a fleet of new gas plants will warm the heart of big frackers like Chesapeake Energy CEO Aubrey McClendon, it could be a disaster for the climate. As I wrote it an earlier post, it is true that burning natural gas – aka methane – releases about half as much CO2 as an equivalent amount of coal. But when it comes to trapping heat, methane is about 21 times as potent as CO2, even though it is stays in the atmosphere a much shorter time. And as it turns out, a lot of methane leaks out into the atmosphere in the course of producing natural gas. Exactly how much, and with what effect, is hotly debated. Some studies have shown that natural gas could, in fact, be worse for the climate than coal. But even if you don’t factor in leakage rates, shifting to natural gas is not going to begin to stop global warming. As a new study by climate scientist Ken Caldeira and tech billionaire Nathan Myhrvold argues, shifting to natural gas “cannot substantially reduce the climate risk in the next 100 years.”

So this new rule is, at best, a baby step in the right direction. As always with the climate crisis, physics is moving much faster than politics. Just yesterday top scientists warned that global warming is close to irreversible now. In the biggest sense, we’re still doing next to nothing to confront this crisis. Global carbon pollution is rising faster than ever, and the weather – to say nothing of our future climate – is getting wilder. The urgency of our situation just underscores the need for an economy-wide price on carbon, or cap-and-trade system, which would impact all major emissions sources and actually limit the amount of carbon we dump into the atmosphere, rather than just speeding the shift from coal to gas.

Still, this is an important moment, a small sign of progress. Goodbye, Mr. Coal. Don’t let the door hit you on the way out.